Hi Sam,
did you know when these problems started? My last (successful) submission to the MAS was on Dec., 3rd (and yet no complaints from customers about crashes), but at the end of November some customers had problems with corrupted receipt files (not missing, but corrupted). A re-download from MAS solved their problem.
At that time local testing a MAS App before submission to Apple started to fail (see: Unable to pre-test app for MAS)
Maybe the whole process at Apple is undergoing some significant changes under the hood…